The present invention relates, in general, to a mechanically operated change-speed gearbox for use in motor vehicles, and more particularly to a shift control apparatus for a change-speed gearbox, including a locking mechanism for preventing a misshift between a forward gear and a reverse gear when actuating a gear selector lever which is operatively connected to a selector shaft.
Locking mechanisms, also known as reverse gear lock-out mechanism, are used in gearboxes to prevent a shift-through from a forward gear into reverse gear, when these gears are positioned in a same linear shifting lane. Erroneous shifting into reverse gear, that may occur if the selector lever were to be moved directly from one forward gear to the reverse gear, are thereby prevented and the gears are protected from damage so that serious damage of the shift control mechanism is avoided. Typically, the reverse gear lock-out mechanism is so structured that the selector lever must be first moved into neutral before clearing the shifting lane to the reverse gear and allowing a shift into reverse.
German Pat. No. DE-C 36 01 954 describes a reverse gear lock-out mechanism having a shift control mechanism with a selector shaft which includes a shifter finger for interaction with a gear shifting gate that is mounted to the housing wall of the gearbox. The shifting gate includes the shifting lane for the gear selection and has a prolongation which accommodates a locking mechanism in communication with a second shifter finger. The locking mechanism includes a plate which is swingably mounted to the shifting gate and held in neutral by a leg spring and swingable in two directions. The plate has a top side formed with a locking cam with a so-called arched catch, for cooperation with the second shifter finger. When changing from the fifth gear to the fourth gear, the second shifter finger strikes against the locking cam to thereby prevent a shift-through along a straight line into the reverse gear which is positioned in the same shifting lane as the fifth gear. The restraining action realizes a diverting of the shifter finger into the neighboring shifting lane. This conventional reverse gear lock-out mechanism suffers the drawback that a great number of components and a substantial space for installation are required because the shifting gate, guiding the shifter fingers which are radially aligned with respect to the selector shaft, is arranged parallel and offset to the selector shaft. As a consequence of the interaction between the shifter fingers and the shifting gate, the manufacture of the individual components as well as the installation and adjustment of the conventional locking mechanism demands high precision.